1. Field of the Invention
The invention relates to differential receivers. More particularly, the invention relates to testing arrangements and methods for verifying proper board connections of differential receivers.
2. Description of the Related Art
Differential receivers are devices configured to receive information transmitted according to a differential signaling method. Differential signaling, which typically is used in relatively high speed signaling, especially when transmitting information relatively significant distances, involves the transmission of two complementary signals over separate conductors. A differential receiver reads the two complementary signals received from a transmission source and provides an output based on the difference between the two complementary signals.
The IEEE 1149.6 Standard for Boundary Scan Testing of Advanced Digital Networks was created to be able to detect the single-ended connection path on a differential input/output (I/O) port or pad. The standard was developed to detect proper termination if an alternating current (AC)-coupled capacitor or a direct current (DC) connection is implemented. In general, one type of boundary scan testing makes use of a plurality of serially connected data storage devices, such as shift registers, and involves loading a value into a register and then applying a certain voltage condition to the associated I/O pad to determine if an open or short circuit exists.
The IEEE 1149.6 Standard calls for a test receiver that behaves as a comparator on a single leg of a differential pair. Conventionally, the test receiver includes a low-pass RC circuit coupled thereto that will time-delay a signal transition with respect to itself so that the test receiver can detect a high or low transition. However, the use of the low-pass RC circuit in the test receiver forces this conventional test implementation to have a custom RC filter and test receiver for each board application. Such need for custom test circuitry inhibits the use of a universal circuit for testing different types of differential I/O ports, i.e., for different board applications. Also, the low-pass RC filter in the conventional test receiver is susceptible to noise, and limits the operating frequency of the test receiver.
Therefore, a need exists for a more robust and simpler implementation and method for the detection of proper external (on-board) connections for differential receivers.